Sorry, guard drake, native to dl 34. Oh, looking at the edit file, Wormtongue has S_HI_DRAGON, which is a joke at cl 21. He is far, far tougher than I was expecting. Really, this is not remotely danger level 21. He's a level 54 monster!
Edit:
Recommendation: make the inner levels deeper, and have an "outskirts" that is shallow, and not guarded by wormtongue. Depth 22-40 isn't much use to a character who can kill wormtongue. This dungeon doesn't make a lot of sense.